DIY

Building my joule thief LED flashlight

imrehorvath, , Leave a comment

Have you ever thought of hand-making your own little flashlight? Actually it’s easy! Well, you need only a few inexpensive and common components to build it.

What’s this?

To put it simple, a “Joule Thief” is an electrical circuit which makes it possible to light an LED with a lower voltage than it would normally need to function.

Use case

I’d like to make a small flashlight which requires only an AA battery (1.5 Volts) to operate.

How to make it?

You will need to wind a ferrite toroid with two wires. It is highly recommended to use two different color insulated wires because you will need to distinguish between them when soldering the parts together. The funny is that you will end up with four leads when done with the winding, but you will need three leads to make the connection to the other parts of the circuit. The trick is to choose two different color wires coming from the opposite side and solder them together. That’s it. Now you have only three leads.

Connect this “double” lead from the inductor to the switch, which is connected to the positive side of the battery in turn.

One of the “single” leads from the toroid should be connected to the base of the transistor through a 1 K resistor. The other goes to the collector.

You need to connect the emitter lead of the transistor to the negative side of the battery to close the circuit.

Components
  • White LED
  • TACT micro switch
  • 1 K resistor
  • 2N3904 transistor (NPN)
  • Ferrite toroid core (14.2X5X9)
  • Wires
  • 1 AA battery holder
  • 50x100mm Stripboard (prototyping PCB)
  • Rubber bands
  • AA battery

Of course you’ll need a soldering iron, solder and a helping hand with a magnifying glass attached too.

The finished flashlight

JouleThief_front JouleThief_side

great Joule Thief maker posts

Read more about the Joule Thief on Wikipedia

Building my joule thief LED flashlight